Wagner is also active in Syria, where it is believed to have as many as 2,500 fighters, and has been placed under US sanctions for its alleged involvement in the Ukraine conflict.

Russia has taken an increasingly prominent role in the CAR over the past year and received UN approval to train and arm the country's army in December.

In 2013, Muslim rebels from the Seleka umbrella group overthrew the president in the majority-Christian country. A band of mostly Christian militias, called the anti-balaka, rose up to counter the rebels.

The continuing violence has left half of the population in need of humanitarian aid.